Euectrocleanuxg  process



Reissues! Dec. 3, 1935 Thomas E. Dunn. Bridgeport, Conn uaignor to TheBallard Company, a corporation of Connectlcut No Drawing. Original No.1,898,765, dated February 21, 1933, Serial No. 618,403, June 20, 1932.Application for reissue February 1, 1935, Serial 12 Claims. (Cl- 204-7)This invention relates to an electro-cleaning process for cleaning metaland has for its object to provide a process for removing the surfacescale and other objectionable .matter from forgings, castings, or thelike.

It is among the prime objects of the invention to provide a cleaningprocess which, while being highly eiflcient andefiective, will avoid theinherent disadvantages of present day mechanical,

:chemical or electro-chemica'l processes, such as their injury to thesurface of the base metal of the object cleaned, and the expense andtime consumed by such operations.

A further object is to provide a. process which .-.is particularlyadapted for the descaling of ob jects having recessed or intricatesurface designs and which in addition to removing scale or surface dirtfrom the work, will act to prevent hydrogen embrlttlement and which willprotect the work against deleterious chemical action, such as pitting oretching, and which will also protect the articles against subsequentrapid surface deterioration.

One highly important object and one which has not been heretoforeachieved is to provide a process which in addition to descaling of thework will provide a highly tenacious and closely adherent metallicprotective film thereover which is I joined to the work surface by analloy-like bond. Among the many advantages of this typeof film bond inaddition to the natural lasting virtue of such adherence is thetranslucent characteristic of the film in thatdefects of the worksurface can be observed therethrough. Another advantage of this type ofbonded film is the provision of a. surface suitable for the reception ofpermanently adherent subsequent coatings or deposits.

Another highly important object of the present invention is to providean electrolytic descaling process of the character disclosed, theelectrolyte of which will remain efficient and effective over a longperiod of usefulness whereby the process is less vulnerable tointerference by ions foreign to those useful to the process. Since withsimilar processes the electrolyte becomes contaminated by a growingconcentration in the electrolyte of ferric ions so that the efficiencyof the process is materially reduced, it is among the objects of thepresent invention to provide a process in which the oxidation of ferrousions to ferric ions is partially or wholly inhibited.

Attention is directed to applicant's Patent No. 1,775,671, grantedSeptember 16, 1930, which discloses a process for acid cathodicdescaling and simultaneous protection of forgings, castings, or

similar scaled metallic articles. This application is a jointcontinuation. of applicant's pending application No. 451,517, filed May10, 1930 and applicants joint application No. 482,151, filed-September15, 1930 and is, therefore, therewith a continuation in part of theapplication which resuited in applicant's prior. patent aboveenumerated, the claims ofwhich broadly cover a process which involvesthe generation of excessive hydrogen at the work whichact s tomechanically detach the scale from theworksurface, and in which thedescaling of any portion of the work surface is followed instantaneouslyby the protection of the cleaned surface by the deposit of a metal film.

The present process has among its objects to partake of the desiderataof the process of the above patent, outstanding among which are that thefinished work is (1) free from pits or etches, (2) free from voltaiccouples-and (3) free from hydrogen embrittlement. In addition to these.virtues, the present process combines with them the advantage ofproducing a. less soluble and more durable protecting film having alighter and brighter appearance and which is thus more pleasingthan-theopaque lead film referred to in my patent; The film; produced bythe present process is not only. harder and free from smut, but isbonded more adherently to the surface, its color and adherence. being avaluable aid to inspection of the underlying body as well as pro, vidinga more presentable and thus-more salable article andone .readily adaptedto-receive sub sequentpermanently adhering coatings produced by hottinning or galvanizing. Another novel as feature of this process is thatthe film produced is susceptible of alloy union with the base metal asdistinguishing from lead which will not alloy with iron. Thus the film,if-not alloyed at the time of deposit, will sounite with the work as aresult of'subsequent heat application. The present process also has theadvantage of retarding the increase of ferric ion concentration of theelectrolyte, thus insuring a longer and/or more highly efficient lifefor the bath. 5 In carrying out the present process I make the work,which is preferably iron or steel, cathode in an 'acid bath whichcontains ions of a metal having an aflinity for iron and which will upondepositwet the iron surface, and thus closeand thus will. wet and alloywith the work surto cause accelerated anode corrosion and sincewiththeuseoftimanodecorrosiontakesplace without the presence ofchlorides, and further, since chlorides attack heating coils usedto warmthe electrolyte and other accessories, they are preferably avoided. Suchchloride free electrolytesarealsocheaperandaresimpiertocom- 'pound.Therefore, I prefer to use the following electrolyte: 10% 8:80 byvolume, 66' B6,, 90% H10, and 3 as. per gal. of sodium sulphate(NaaSOa-IOHaO).

While this composition illustrates one possible electrolyte, it will, ofcourse, be understood that different components may be used and widelyvarying proportions substituted. Thus, when using zinc I prefer tosubstitute sodium or mercuric chloride for the sodium sulphate. The widedeparture from the specified formula to which the process is susceptiblehas a distinct advantage in that it does not require the close chemicalcontrol, which is advisable in other processes.

While the process will function properly by the introduction of the ionsof the metal to be deposited through the inclusion in the electrolyte ofsalts thereof, I prefer for the sake of automatic control, as well asfor the sake of simplicity and" economy, to introduce the ions of themetal by the use of anodes formed thereof. The process, therefore,departs from the teaching of my original patent in that I use inconJunction with anodes of the metal to be plated, insoluble anodeswhich will not give to the solution ions capable of electrolyticdeposition on the cathode. Thus, with the metals mentioned, I prefer tohave approximately only two percent of the total anode area formed ofthe metal which is to form the film. The remaining anode area requiredfor the sufiicient excitation of the bath is-preferably formed ofinsoluble anodes. A further virtue of theuseofalargeareaol' insolubleanodes is that since no energy is required to disintegrate and ionizemetal at the surface of such insoluble anodes, it follows that for agiven energy input, the volume of hydrogen liberated at the cathode isincreased and consequently the efficiency of the process is greater thanwhen all the anode area is formedof the metal used for the protectingfilm. Intcarrying out the process, I prefer to use cathode currentdensities approximately 50-100 amps. per square foot of work surfaceunder treatment.

It has been found that the efilciency of the process decreases at asubstantially inverse ratio to the increase of ferric ion concentration.Therefore, the present invention embraces the use of anodes at whichreactions tend to inhibit the oxidation ofthe ferrous ions to ferricions. The electrolyte oi the present process has thus been found to havematerially longer and/or more highly efiicient life than the electrolyteof a process using lead. This advantage in the present process is deemedto be the result not of differences in electrolytes but as a result ofmarked diiferencesin the anode reactions of this process. Theoretically,among these differences is that in the use of this process, a colloidalshielding film of metastannic acid is formed on the insoluble anodesurface. This film prevents the electrolyte bearing ferrous ions fromcoming into direct contact with the surface of the anode where theferrous ion content would be actively oxidized to the ferric state.However, when lead is used as the protective metal film and the anodesurface is composed of lead or a lead alloy, no such shieldingdiaphragm-like film is formed and 5 consequently the electrolyte bearingferrous ions readily come into direct contact with the surface of thelead anode. Consequently, the ferrous ions are rapidly oxidized to theferric state. Furthermore, the surfaces of lead anodes become coatedwith lead peroxide (PbOz) which, as is well known, exerts a strongcatalytic action fa-g. voring oxidization and therefore, with leadanodes, two distinct anode conditions are obtained both stronglyfavoring the rapid increase of the ferric ion concentration of theelectrolyte. This is' in sharp distinction to the highly favorable anodereaction of this present process, which leads to the formation of anenshrouding metastannic colloidal diaphragm-like film which tends toingo hibit the oxidation of the ferrous ions.

When a scaled article is introduced in the electrolyte as cathode and issubjected to high current densities, excessive quantities of hydrogenare vigorously liberated at the surface of them; work. The action of thehydrogen, either along, or in conjunction with, chemical attack, actsmechanically to wedge or crowd on the scale, leaving a denuded cleansurface area. Since the clean surface provides a direct relativelylessso resistant electrical path through the base metal, the deposit ofa metal film such as tin, will take place immediately thereon, and sincesuch deposit acts to increase the polarization at that portionelectrolytic as of the surface, the concentration of action will shiftor be thrown to other less polari'zed portions of the surface. Thisso-called throwing" characteristic of the process has, in connectionwith the use of metals, such as tin,

. having lower over-voltage than lead and having 40 an aifinity foriron, 8. distinct difierence from the reaction of lead ions at thecathode. Thus, while it would appear from a consideration of throwingpower alone that such metals would be less efilcient than lead, it willbe apparent that less energy is required at the cathodes for theirdeposition, because their hydrogen over-voltage is less, and the naturalafilnity of tin or like metals for iron will also aid in the reactionandin practice tends to offset the lower throwing power.

In the operation of the process, it is found that the initial strata ofthe film deposit actually tend to wet or alloy with the iron surface,the resultbeing that in place of the deposit of a mechanically bondedand thus less adherent lead film, there is a positive tendency of thetin molecules to wet and spread over. the surface of the base metal andto join therewith by metallurgical union. Another feature of the processis that the film is of a metal which will readily form a true alloy withthe base by subsequent heating.

The process, therefore, produces a bimetallic article, the outer surfaceof which is an integral portion of the whole and yet formed of adifferent metal. It will, of course, be understood that with the use ofthe high current densities specified, there may be deposited on top ofthe alloy-- like film, loose, spongy deposits of the pure metal such astin or zinc.

flnished article presents a pleasing bright surface which is highlyadvantageous in certain fields. This surface has a high scratch hardnessand is free from the graphite-like soiling characteristic of leadsurfaces. The integral bonding of the film is also of major importancein connec: tion with subsequent treatments. such, for instance, hottinning or galvanizing.

From a consideration of this specification, it will be understood thatthis process is not restricted to the use of the specific metallic ionsreferred to.but is understood to be generic in its teaching of the useof ions having an amnity for or being capable of alloy bonding with theto inhibit the oxidation of ferrous to ferric ions in the electrolyte.As indicated, the characteristics of the hath, not only as to theproportions of the ingredients, but as to the ingredients themselves,can be widely varied without departure from the spirit or scope of theinvention.

Having thus set forth the nature of my invention, what I claim is:

1. A method of cleaning surfaces which includes the step of removingsurface foreign matter by the cathodic production of hydrogen at thework and simultaneously protecting the cleaned surface by the depositthereon of tin in an acid electrolyte in which there are soluble andinsoluble anodes.

2. A method of cleaning surfaces which includes the step of removingsurface foreign matter by the cathodic production of hydrogen at thework and simultaneously protecting the cleaned surface by the depositthereon of tin in an acid electrolyte in which there are soluble andinsoluble anodes, the former giving to the electrolyte ions capable ofdepodting on the cleaned work simultaneously with the cleaning.

3. A method of cleaning surfaces which includes the step of removingsurface scale by subjecting the work to cathodic action in an acidelectrolyte in which there are soluble and inmaintaining a desired tinion concentration for simultaneously depositing during the cleaning, ametallic protective film on the work.

4. A metal cleaning process which includes surface the cathodicproduction of hydroi n at the work and simultaneously protecting thecleaned surface by the deposit of tin thereon in an acid electrolytecontaining salts of tin which by the action of the process automaticallyforms a shielding diaphragm of metastannic acid about an'insoluble anodeto, inhibit oxidation of low valence ions which may be formed fromdislodged foreign matter.

5. A process as set forth in claim 4 characterized by the use of asoluble anode including tin to continuously supplying tin ions to thesolu- 'tion.

6. A process as set forth in claim 4 characterized by the use of bothsoluble and insoluble anodes the former providing tin for the deposit onthe work and for the formation of the metastannic acid film. 4

I. The process of electrolytically removing scale from ferrous metalsurfaces and simultaneously base metal of the work and to metals whichtend soluble anodes the former including tin and pro-, viding therequisite surface area for continuously electro-depositing tin thereoncomprising subjecting said surface to the action of a bath containing ascale-removing concentration of a pickling acid while passing currentthrough the bath to the surface as cathode, to thereby evolve 5 hydrogenat said surface, the bath also containing such concentration of tin saltthat the current employed will deposit a continuous adherent coating oftin on time required from. 1

8. The process of treating articles of ferrous metal to remove scalecomprising placing the article in a bath containing a sufficientconcentration of pickling acid to effect scale removal, passing throughthe bath to the article as cathode an electric current of such strengthas to cause copious evolution of hydrogen at the cathode to assist inremoval of scale, maintaining in the bath a concentration of tin saltsof suchlo character that tin can be deposited therefrom by the saidcurrent, and so adjusting the concentration of tin salts, the acidity,current density and temperature that a thin deposit of tin forms uponthe scale-free surfaces of the article in as substantially the timerequired to remove the scale and of substantially only the thicknessrequired to protect the cleaned surface from attack by the acid.

9. The process of cleaning and coating an arso ticle having ferrousmetal surfaces comprising immersing the article in a bath containing apickling acid in such concentration as to remove scale and also a tinsalt from which tin may be said surface in substantially the for theremoval of scale there- 1 electrolytically deposited. supplying electriccuras rent to the article as cathode in the bath in quantities betweenand amperes per square foot of cathode surface, the acid concentrationbeing maintained such as to effect electrolytic pickling with thecurrent employed and the con- 0 centration of tin being maintained suchas to effect deposits of tin upon the cleaned surfaces sufficient toprotect the cleaned surface from further attack by the acid;

10. The process as set forth in claim 7, the. bathcontaining sulphuricacid to the amount of approximately 10% by volume.

11. The process of electrolytically removing scale from ferrous metalsurfaces and simultaneously electro-depositing tin thereon comprising .9subjecting said surface as cathode in an acid electrolyte. maintainingfor the electrolyte a continuous supply of tin, passing current throughthe bath to thereby evolve hydrogen at said surface for removing scaleand depositing a continugs ous adherent coating of tin on said surfacein coniunction with the scale removal therefrom.

12. The procws ofnelectrolytically removing scale from ferrous metalsurfaces and simultaneously electro-depositing tin thereon comprising assubjecting said surface as cathode in an acid electrolyte containing tinto the action of current passing through the bath whereby the currentemployed will evolve hydrogen at said surface for removing scale, willdeposit a continuous adherent coating of tin on the surface-inconjunction with the scale removal and will automatically provide acontinuous supply of tin for the electromouse a. norm.

